The present invention relates to an orthodontic appliance adhered to teeth, such as a bracket, buccal tube, sheath, button or lingual attachment.
Orthodontic appliances for use in orthodontic treatment been widely known, which comprise a main body capable of maintaining an archwire and a bonding base connected to the main body and capable of adhering to teeth. Those orthodontic appliances include bracket, buccal tube, sheath, button, lingual attachment and the like, and are appropriately selected according to orthodontic treatment methods.
In particular, the bracket is most ordinarily used in the following manner. The bracket is directly adhered to the patient""s teeth with bonding base being inside. Archwire is mounted on the bracket thus adhered. As a result, external force is applied to malaligned teeth by the archwire, thereby correcting such malaligned teeth.
Metal brackets have conventionally been known as the ordinary bracket. Orthodontic appliances formed from transparent or white semi-transparent materials such as ceramic bracket or plastic brackets have recently been used for the purpose of improving aesthetic properties.
However, the ceramic bracket made of aluminum oxide or zirconium oxide is extremely hard in comparison with metal bracket, and is also harder than enamel of the teeth, so that there is the possibility of abrading enamel of the opposite teeth contacting the bracket when occluding. Especially, a deep bite has been a tabooing case evading the use of the ceramic bracket. To overcome such problems, U.S. Pat. No. 4,950,158 proposes a method of interposing an elastmeric cushion at a tiewing of incisal side.
In case of adhering a bracket having a slot in a main body and inlaying the archwire in the slot to perform the correction of dentition, the archwire should be slippery to the slot, because the teeth row is corrected by a restoring force of the archwire. However, the archwire is difficult to slide to the slot provided in the ceramic bracket, and friction between the bracket and the archwire is large, so that a problem occurred that it is difficult to exactly perform a desired correction of dentition. The main reason for this is assumed that since the ceramic bracket is very hard, the archwire creates biting at an end portion in the mesiodistal direction of the slot.
In view of the above problems, U.S. Pat. Nos. 5,358,402 and 5,380,196 disclose technologies, that a metal slot liner is attached to the ceramic bracket by means of, for example, brazing in order to improve the sliding property of the archwire within the slot. However, the ceramic bracket comprising inorganic materials such as aluminum oxide or zirconium oxide are difficult to bond to organic adhesives generally used for the orthodontic purposes. Therefore, it was necessary to apply a silane coupling agent to the bonding base, or weld glass frit or glass beads on the bonding base to form a mechanical lock thereon, thereby increasing bonding force to the organic adhesives. Treating the bonding base was a factor to increase production cost of the ceramic bracket.
When the bracket adhered on the teeth is debonded after orthodontic treatment, if the bracket is made of a metal, such a bracket can be debonded as if turning over the bonding base without injure the teeth. On the other hand, the ceramic bracket is harder than the metal bracket and the bonding base has an integral structure of the main body and has high rigidity. Therefore, extremely large force is required to debond the bracket, and there is the possibility of injuring enamel of the teeth. To overcome those problems, U.S. Pat. No. 5,439,379 proposes a method of crushing ceramic bracket at a central groove and debonding the same. Further, technologies of shielding a surface of a bonding base having dimples (U.S. Pat. No. 4,936,773) and a central part of a bonding base with an inert paint (U.S. Pat. No. 5,269,680) are to positively control a bonding/debonding strength.
On the other hand, the plastic bracket has a problem that the bracket is liable to deteriorate by absorbing water in the mouth during the orthodontic treatment and it is also liable to disintegrate before the completion of orthodontic treatment. In addition, the plastic bracket is liable to adsorb coloring agent contained in foods and drinks by water absorption, resulting in a further problem in deterioration of the aesthetic appreciation due to such a discoloration.
Polycarbonate brackets are widely known as such a plastic bracket. However, since such a bracket does not have sufficient strength to torque by rectangular archwires or ligation of a ligature wire, the bracket is generally reinforced with a metal insertion. For example, U.S. Pat. Nos. 4,299,569 and 5,254,002 disclose plastic brackets having a metal slot liner as the insert arranged in mesiodistal direction of the bracket. Further, U.S. Pat. Nos. 5,595,484, 5,597,302 and 5,692,898 disclose plastic brackets formed by inserting metal members having U-shaped section in a direction crossing the slot.
Polycarbonate brackets having glass fibers mixed therewith for strength improvement are also known. The glass fibers contributes to improve strength of the bracket, but there is the problem that solvent cracks tend to occur due to influences by organic solvent components of an adhesive used for orthodontic application. It has been clinically known that the glass fiber reinforces the polycarbonate bracket, but on the other hand increases internal stress in the polycarbonate when molding, and microcracks occur due to the presence of a solvent in the adhesive or water-invasion with the passage of time, and as a result, the polycarbonate bracket deteriorates as being disintegrated.
A glass bracket is known as means for overcoming the problems involved in the ceramic and plastic brackets, and U.S. Pat. No. 5,261,814 discloses a bracket in which surface layer is crystallized under compression stress to form a reinforcing layer and the inside thereof is constituted of amorphous glass comprising the following compositions: SiO2 55 to 70%, Al2O3 15 to 28%, ZnO 0 to 14%, Li2O3 0 to 7%, Na2O 0 to 7%, K2O 0 to 3%, BaO 0 to 7%, MgO 0 to 7% and TiO2 0 to 7%.
However, this bracket is expensive because it is prepared from a glass sheet by a supersonic abrading process, a diamond cutting process or the like. Further, it is technically difficult to control thickness of the surface crystallized layer, and unevenness in thickness results in decreasing transparency (devitrification) and strength.
U.S. Pat. No. 5,795,151 describes a bracket comprising a diopside crystallizing glass (glass composition: SiO2, MgO, Al2O3 and TiO2). However, this bracket contains Al2O3 and TiO2 in high contents. As a result, hardness of such a crystallizing glass is higher than that of the enamel of a natural tooth and there is the possibility of abrading enamel of the opposite teeth.
U.S. Pat. No. 4,784,606 describes a bracket comprising a glass tempered by ion exchange, where Lixe2x80x94Alxe2x80x94Si glass is dipped in a molten salt bath for 2 to 24 hours at temperatures higher than a strain point of the glass but lower than a softening point thereof, thereby obtaining the glass tempered by Naion. However, there is a problem that the ion-tempered layer is thin, and the bracket is worn in an early stage and is broken by occlusion or ligating.
U.S. Pat. No. 4,784,649 describes a bracket comprising a glass of a double crystal structure for the purpose of increasing strength. This glass has a large crystal structure in the inside of the glass, and has a small and flat crystal layer on the surface thereof, but a production process thereof is complicated. Further, not only cost is high but also strength is insufficient.
Thus, the glass bracket has disadvantages that its production process is complicated, its production technique is difficult, its production cost increases, and its strength and durability are insufficient as the orthodontic appliance.
The above-described problems occur all over the orthodontic appliances of the type which directly adhere to tooth crowns such as buccal tube, sheath, button or lingual attachment, in addition to the brackets.
The invention has been made in view of the above-described problems in the related art.
Accordingly, an object of the invention is to provide an orthodontic appliance having all of the following advantages 1) to 9):
1) production cost can be decreased;
2) aesthetic appreciation is excellent;
3) sufficient strength and durability are provided as the orthodontic appliance;
4) an allergy causing substance is difficult to generate;
5) the adhesion to the teeth is secured;
6) the opposite teeth are less to be worn during orthodontic treatment;
7) plague causing decayed teeth or periodontal diseases are difficult to adhere to the bracket during the orthodontic treatment;
8) debonding from the teeth is easy after the orthodontic treatment; and
9) in case that the orthodontic appliance allows engagement with the archwire for straightening the teeth, the sliding property is excellent to the archwire.
The invention provides an orthodontic appliance comprising a main body for orthodontic treatment and a bonding base connected to the main body and capable of adhering to teeth, wherein the main body and the bonding base each comprise a calcium phosphate crystallizing glass. Thus, because the main body and the bonding base each comprise the calcium phosphate crystallizing glass showing white and semi-transparency, the aesthetic appreciation of the orthodontic appliance is excellent.
Further, the bonding base comprising the calcium phosphate crystallizing glass does not require any special treatment as seen in ceramic brackets and can be securely adhered to the teeth with an adhesive for the orthodontic purpose, and the production cost of the orthodontic appliance can be decreased.
The calcium phosphate crystallizing glass orthodontic appliance does not require a metal insertion as seen in the plastic orthodontic appliances and also does not require any special treatment of forming a reinforced layer as seen in the conventional glass orthodontic appliance, but it has enough strength and durability as the orthodontic appliance. Therefore, the production cost of the orthodontic appliance can be decreased.
Further, since hardness of the calcium phosphate crystallizing glass can be determined so as to be equivalent to the hardness of enamel of the teeth, the opposite teeth can be prevented from wearing during the period of orthodontic treatment, and the orthodontic appliance can be easily debonded from the teeth without requiring excessive force after the orthodontic treatment.
The orthodontic appliance, in particular the tiewing, is sometimes disintegrated by unsuitable debonding operation, giving undue torque by the archwire, or unreasonable use of the wire cutter when cutting the ligature wire after ligating the archwire and the orthodontic appliance.
Even in such cases, the calcium phosphate crystallizing glass orthodontic appliances are comparatively grain-like in broken sections different from sharply broken sections as seen in soda lime glass widely known as general glass, and does not injure the mucous membrane in the mouth.
In addition, plague causing decayed teeth or periodical diseases is difficult to adhere to the calcium phosphate crystallizing glass orthodontic appliance.
According to the calcium phosphate crystallizing glass orthodontic appliance, it is not necessary to positively insert the metal liner as described above, and it is possible to provide the orthodontic appliance difficult to generate the allergy causing substance as represented by, for example, nickel.
The preferred embodiments of the invention are described below.
The calcium phosphate crystallizing glass comprises CaO 10 to 60 wt %, P2O5 25 to 85 wt %, Al2O3 5 to 25 wt % and Li2O 0.01 to 5 wt %. By preparing the calcium phosphate crystallizing glass having the above composition, the orthodontic appliance has high crystallizing rate particularly in crystallization, generates a fine and close crystallized structure, obtains high strength and a proper hardness not causing dental attrition to the enamel of the teeth, and has the transparency approximate to the enamel in spite of high crystallinity.
The orthodontic appliance is constituted such that Vickers hardness Hv based on JIS Z2244 of the calcium phosphate crystallizing glass is 4.5 GPa or lower, and bending strength based on JIS R1601 of the calcium phosphate crystallizing glass is 100 MPa or higher. According to this constitution, Vickers hardness of the calcium phosphate crystallizing glass is 4.5 GPa or lower, and is not too hard in comparison with Vickers hardness Hv (around 3.4 to 3.8 GPa) of the enamel of the teeth. Thus, during the orthodontic treatment, the possibility of injuring enamel of the opposite teeth can be securely decreased, and after the orthodontic treatment, the orthodontic appliance can be easily debonded from the teeth without requiring excessive force.
The bending strength of the calcium phosphate crystallizing glass is 100 MPa or higher, so that the orthodontic appliance has the sufficient strength to the torque by the archwire or the ligation of the ligature wire, and the possibility of disintegrating the orthodontic appliance during the orthodontic treatment can be surely decreased.
The main body and the bonding base are integrally formed with the calcium phosphate crystallizing glass having the same components, and the orthodontic appliance is constituted such that adhesive strength between the teeth and the bonding base is 7 MPa or higher per unit area. By making the adhesive strength 7 MPa or higher, even if a patient takes an ordinary meal, the adhesion can be securely maintained for a period of 18 to 24 months, which is considered as a general period of orthodontic treatment.
Surface roughness based on JIS B0601 of the bonding base is 10 xcexcm or more. According to this feature, a substantial adhesion area between the bonding base and the adhesive for the orthodontic treatment is increased, and at the same time an anchoring effect can be obtained, so that the orthodontic appliance can be more securely adhered to the teeth. The surface roughness of the above-described range can be suitably accomplished by an ordinary phosphorous acid etching. This phosphorous acid etching can easily be operated by a doctor at a chair side, and the bonding base surface of an orthodontic appliance is made rough by sandblasting and then subjected to the phosphorous acid etching as a pre-treatment of adhesion. This is very useful to increase the adhesive force.
The main body has slots as orthodontic means. According to this constitution, the slot comprises the calcium phosphate crystallizing glass, and when the archwire is inlaid in the slot for performing the orthodontic treatment, the sliding property of the archwire to the slot is equal to or more than that of the metal slot and is excellent. In particular, it is possible to provide the orthodontic appliance difficult to generate the allergy causing substance as represented by, for example, nickel.
The orthodontic appliance is constituted such that dynamic frictional force when an archwire is pressed against the bottom of the slot at 1.96 N (200 gr), is 0.98 N (100 gr) or lower. According to this feature, the sliding property of the archwire to the slot can be securely made excellent.
The slots are provided in the inside thereof with a metal slot liner of U shaped cross section.
The reinforcement generally regarded as being essential, of the plastic bracket by the metal insertion tends to decrease the aesthetic appreciation and increase the production cost. Further, if the insert is made of a stainless steel, metal-allergy is caused by nickel or chromium.
However, the calcium phosphate crystallizing glass has enough strength in comparison with plastics, and the reinforcement by the metal insertion is not always necessary, but depending on kinds and shapes of the teeth to which the bracket is adhered, and types of orthodontic treatment, when it is desired to increase strength of the bracket, the arrangement of the metal slot liner is effective.
According to the above constitution, the sliding property of the archwire to the slot is excellent, and the orthodontic appliance of high strength can be provided.